On January 7, 1997, approximately 1200 mountain standard time, a Cessna TU-206, N717CM, collided with trees while attempting to reverse course in a mountain valley about 15 miles east of Cascade, Idaho. The airline transport pilot received serious injuries, his two passengers received minor injuries, and the aircraft sustained substantial damage. The Part 135 charter flight, which departed McCall, Idaho, about one hour prior to the crash, was en route to a remote mountain airstrip at the time of the accident. The pilot was operating in visual meteorological conditions, on a company VFR flight plan, at the time of the accident. The ELT was not activated by the crash, but was turned on by the pilot after the aircraft impacted the terrain. In a discussion with the FAA, the pilot said that he was approaching a mountain pass in hopes of flying through it to his destination. As he approached the pass, he determined that there was not enough clearance between the terrain in the pass and the overcast above. He therefore elected to reverse course, and return to Boise, Idaho. He said that he was about 100 to 150 feet above the terrain during the course reversal, and that he had slowed to 65 knots and added 20 degrees of flaps. At about the time he rolled out from the course reversal maneuver, the aircraft "...sank or settled..." into the trees. As it sank past the top of the trees, the pilot reached over and slapped the flap switch to the full-down position. He later said that, although he did not look at the flap switch, the amount of distance it moved to get to the full down position made him think that possibly the passenger in the right front seat may have accidentally moved the flap switch to the full-up position by unknowingly bumping into it. Although he was unable to determine for sure that the switch had been moved, he thought that possibly the sinking may have been initiated by such an event.